The traditional optical or electrical connector is a monolithic device, optimized for the delivery of a single signal type—either optical or electrical. There are reasons for this traditional separation of connectors by signal type. First, most applications require only one type of transmitted signal, and thus do not demand the additional design and materials expense involved in hybrid connections. Second, inherent features required for good electrical connections (e.g., good physical contact with contact element wiping, low axial positional mating accuracy, and no need of contact finishing after assembly) are different, and often contrary, to those features required for good optical fiber coupling (avoiding physical contact which damages fiber faces, high axial positional mating accuracy, and required post-assembly fiber-end finishing steps).
These limitations and requirements are best appreciated by examining the source of such differences between optical and electrical connections during mating and assembly.
First, consider the presence or avoidance of physical contact during mating. Electrical connections generally require good physical contact in order to achieve reliable, low-resistance current flow. Metallic contacts also tend to accumulate surface deposits and corrosion over time, so a “wiper” effect is usually incorporated into the physical make-and-break actions to facilitate ongoing contact cleaning. In contrast, good physical contact between optical fibers is generally to be discouraged because the layered glass faces of fibers are fragile. Direct physical contact between optical fibers damages the cladding that keeps light within the fibers, scratches the optical fiber face where light is transmitted, or shatters the fiber body entirely, all of which reduce fiber light transmission or renders the fiber useless.
Second, consider the axial (Z-axis) positional accuracy required during mating. Electrical pin and socket connections, once inserted part way, usually continue to work well as the elements are pushed farther together. In fact, a bit of additional insertion in electrical contacts usually leads to improved contact due to the increased contact surface area and wiping effects. Therefore, there is little Z-axis positional accuracy typically required to make an electrical connection work well. This permits electrical contacts to be manufactured cheaply in large arrays using low-axial-accuracy metal pins and sockets, such as the standard D-pin connectors used in the computer industry which have 9 to 100's of pins in a planar (flat XY-axis plane perpendicular to the axis of insertion) arrangement. Such planar electrical contacts typically also have lateral pin wiggle—easily demonstrated in a 9-pin standard D-Pin connector in which the male pins each show millimeter lateral movement if physically perturbed.
In contrast, optical connectors are not so tolerant of error. Fiber connections have lateral (XY-axis) and axial (Z-axis) positional mating accuracy requirement as much as 1,000-fold more precise than for the above-described electrical connections. An optical fiber's tolerance for positional error is typically very low for several inherent reasons. First, axial (Z-axis) movement of optical fibers away from each other results in a loss of optical coupling; while axial movement toward each other must be carefully limited in order to prevent collisions between the fiber ends. Such collisions can seriously damage most optical fiber faces. Second, a seemingly minor lateral positional misalignment of a pair of optical fibers typically leads to huge fiber coupling losses. For illustration, a mere 0.004 inch lateral offset between a 100 micron pair of multimode fibers can lead to a complete loss of transmitted light.
Because of this need for micron alignment between coupled optical fibers, fiber connections typically require high-precision components in the connector. These precision components—including laser drilled ferrules and milled stainless-steel couplers—translate to a high connector cost. For example, a pair of industry-standard SMA-type optical plugs and central mating dual-female coupler connector, allowing for the joining of only a single pair of fibers, retails at many times the price of a pair of 25-pin D-type electrical array male/female connectors.
Third, one must consider the accessibility of the contacts during assembly and finishing. Electrical pins are typically shielded or hooded, and the sockets recessed, to prevent wire to wire shorting. In contrast, optical fiber ferrules must typically protrude beyond any protective holders in order to allow for fiber finishing (such as gluing, sanding, and polishing) after a new, bare optical connector is stuffed and glued with an optical fiber.
All told, when taking into consideration the above inherent limitations, electrical and optical connectors have physical contact, positional accuracy, and post-assembly requirements that come directly into conflict, and such conflicting requirements are not readily simultaneously satisfied.
The above limitations of conventional connectors are apparent in the art.
Hybrid optical and electrical connectors are known. Such deployments are most typically planar (XY-axis), in which the mating elements form a face that is flat and perpendicular to the axial mating axis. For example, WO 01/042839 and U.S. Pat. No. 6,612,857 teach independent detachable electrical or optical assemblies that are combined into a single hybrid connector. U.S. Pat. No. 6,599,025 teaches a hybrid with the optical fiber positioned between the electrical elements of a standard connector. U.S. Pat. No. 6,588,938 teaches a hybrid housing with planar arrays of electrical contact maintained by springs. An independent element hybrid commercial product is known (Miniature F7 Contact for Multi and Hybrid Fibre Optic Connectors, sold by Lemo S. A. of EcublensSwitzerland). These Lemo connectors, by failing to simultaneously optimize the different requirements of optical and electrical connections through Z-tolerance, remain expensive (greater than U.S. $100 per connector). All of these hybrid devices remain simple, non-optimized devices that suffer from the drawback that they use independent, standard, planar coupling elements without optimization of the differing and conflicting electrical and optical mating requirements, and do not suggest or teach a need for increased axial tolerance, all of which is required for low-cost simultaneous mating of both the electrical and optical signals.
Axial (Z-axis) deployment of the electrical contacts along a shaft is a known, though uncommon, alternative to planar contact deployment. U.S. Pat. No. 4,080,040 teaches a longitudinal (axial) arrangement of multiple electrical contact elements along a patch-cord plug and receiving jack, but does not teach how to reduce the axial positional accuracy requirements of the connector through use of floating or lens-coupled elements for fibers in a hybrid design. Combination of this or other axial plug and socket arrangements with optical fibers, as is taught in the cited hybrid connectors above, would be insufficient to achieve Z-tolerance, as a need for Z-tolerant elements to increase axial tolerance is neither taught nor suggested in either body of art.
Optical elements facilitating good fiber coupling along with reduced axial mating accuracy are known. U.S. Pat. No. 5,259,052 teaches a limited-movement floating ferrule that is used to couple two fiber optic plugs. U.S. Pat. No. 6,550,979 teaches a spring-coupled ferrule which urges the ferrule holder in a direction axially toward the mated fiber. However, these are free standing optical elements, without consideration of the design requirements of simultaneous electrical connections, and therefore combination with known hybrid designs is non-trivial. These floating device elements neither teaches nor suggests combining a floating optical element into a hybrid electrical/optical connector that simultaneously optimizes both electrical and optical mating in the presence of the floating elements, a non-trivial manufacturing step.
Each of the above connector systems and methods suffer from one or more limitations noted above, in that they do not incorporate Z-tolerance into both optical and electrical connecting elements (e.g., do not incorporate improved axial tolerance at all, or are not combined into a single, integrated connector that simultaneously optimizes the mating requirements of both the optical and electrical connections), which makes manufacturing and assembly of a hybrid connector technically difficult or expensive.
None of the above systems suggest or teach efficiently combining optical and electrical contacts into a single hybrid connector device optimized for both electrical and optical connections with both (a) a Z-tolerant coupling for the optical elements, and (b) a Z-tolerant coupling for an axial electrical array, together resulting in a low-cost of manufacture, ease of assembly, and single connector ease-of-use. A hybrid electrical and optical shaft and socket connector incorporating a Z-tolerant axial electrical array integrated with a Z-tolerant floating or lens-coupled fiber array has not been taught or suggested, nor to our knowledge has such a tool been previously successfully manufactured and commercialized.